THE THYROID GLAND IN SELACHII. 4I 



the gland. The indentations and consequent traces of lobuhza- 

 tion conform closely to the areas of distribution of the main 

 vessels. The lower, nearly isolated portion of glandular tissue 

 is supplied by a branch from the right mandibular artery which 

 enters the gland on its ventral aspect. The partially detached 

 portion of tissue is placed close to the point of entrance of this 

 vessel and is therefore supplied by the right thyroid artery and 

 not by the left, the vessel entering at the free end of the partially 

 detached lobule; on the left this lobule is continuous with the 

 body of the gland but does not, as one might expect, derive its 

 blood supply therefrom. The right thyroid artery also sends an 

 anterior branch to supply the right posterior third of the main 

 portion of the organ. The remainder of the gland is supplied by 

 a corresponding vessel, a branch of the left mandibular artery, 

 whose area of distribution is much more extensive than that of 

 the right thyroid artery ; it enters the dorsal surface of the 

 thyroid gland. 



The arterial connections were traced with the aid of injections 

 of India ink into the conus arteriosus or into the cardiac ventricle 

 of a freshly opened fish by means of a hypodermic syringe hav- 

 ing a needle of very fine caliber. The continued contractions of 

 the ventricle were sufficient to auto-inject the vessels under 

 consideration. 



